Many types of valves, such as ball valves, butterfly valves, gate valves and the like, which normally seal by means of an elastomer seal ring, have provision for metal-to-metal back-up seals which take over in the event that the main, elastomer seal is destroyed by fire or intense heat. In the case of an expansible tube type valve, such as that shown in Gerbic U.S. Pat. No. 3,669,142 granted June 13, 1972, the seal medium is an elastomer tube and, in the event that the tube is destroyed, the entire sealing medium is lost. In the event that the fire occurs in the pipeline in which the expansible tube valve is installed, and flames enter the housing of the expansible tube valve, there is little that can be done to prevent destruction of the seal. However, valves of this type are frequently used in refineries, pumping stations and the like where a fire, generating intense heat could occur in a nearly pressure vessel or pipeline other than that in which the expansible tube valve is installed. Such fires could heat the metal of the valve body to a level that destroys or damages the expansible tube, even though the fire does not impinge directly upon the tube itself.